Whether it's steak and lobster or linguine and clams, shellfish is a popular choice at market seafood counters or restaurants. Shellfish can be divided into two main categories: crustaceans and mollusks, and due to the vast size of this topic, this will be the first of three instalments.

All shellfish are invertebrate sea creatures, meaning that they do not have an internal bone system like fish, which are called vertebrates. Almost all shellfish have a hard outer shell that protects their soft bodies from predators and the environments they thrive in. Crustaceans include crabs, lobsters, shrimp and crayfish, among others.

Buying shellfish live is almost always preferred, but many don't have this option at their marketplace. When live is an option, it is usually only crabs and lobsters that are available.

There are many ways to cook a live crab or lobster. The most common way is to submerse it headfirst into a pot of boiling water to kill it instantly. Crabs are then boiled for about six to 10 minutes, depending on their size, and lobsters are usually five to six minutes per pound.

Due to the labour required in picking the meat from crabs, they are almost always cooked this way rather than trying to extract raw flesh which is more difficult.

Another option for killing lobsters is to hold it down firmly on a cutting board and plunge the tip of a chef's knife into the head before cooking it. This should be done immediately before cooking it to ensure optimal freshness and flavour, as the rule of thumb for raw crab or lobster is to cook it live. Raw crab and lobster flesh deteriorates very rapidly.

Lobsters are also very tasty if split in half and opened up, brushed with oil, lemon juice, and seasonings and then grilled on the barbecue. When splitting in half, you can cut right through to serve as two halves, or cut from the underside but not all the way through the top shell and serve as a whole split lobster. If prepared in this manner, you will want to weigh down the tail portion as it will curl up and lose contact with the grill. Another way to avoid this is to cut the tail section completely through while leaving the body halves connected by the top shell. This way you are able to curl the tail to the sides of the lobster and should not need to be weighted down. With either grilling option, the large claws should be cracked beforehand as this will assist in cooking the claw meat at the same speed as the exposed body and tail flesh.

When working with or eating whole crab or lobster, the stomach in both cases is located just behind the eyes, and should be removed and discarded. With crabs, the feathery gills located on each side of the body under the shell are also discarded.

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